In current cellular communication systems, pedestrian users will access the mobile cellular network. This mobile cellular network provides continual overhead measurements used by the system to maintain channel quality or perform hand-off functions. Since these measurements require the same amount of processing whether the user is mobile or not, a pedestrian user is charged the same fee for using their phone as the user who is mobile.
Therefore, there exists a need in the industry for a personal communication system (PCS) which would provide a low tier system for pedestrian users at a reduced cost. The low tier system would provide access via radio frequency (RF) link to a basic cellular network which may or may not provide hand-off capability. For purposes of this discussion, a pedestrian user is one who roams slowly (10 kph, kilometers per hour, or less) as opposed to a mobile (up to 100 kph or more) user.
In order to avoid the necessity of having two separate subscriber units (handsets), it is desirable to provide a dual mode network in which only one subscriber unit is required, such as the network described in the DUAL MODE COMMUNICATION NETWORK patent application, incorporated herein by reference, described above.
Once such a network is established, there exists a need to provide a method of selecting which system in the dual network will be used to originate a call. Along the same lines, it will also be desirable to transfer an existing call between the two systems in the dual mode network. Such as, for example, in situations where a user is currently conducting a call while driving in a car. This call would normally be connected in the high tier, more expensive system. When the user stops the car, it would be desirable to have the call transferred to the low tier, more economical system.